CN110106470B

CN110106470B - Preparation method of low-stress diamond-like carbon film

Info

Publication number: CN110106470B
Application number: CN201910348527.6A
Authority: CN
Inventors: 李党娟; 吴慎将; 王娜; 苏俊宏; 徐均琪; 王稳奇; 时凯; 王佳超
Original assignee: Xian Technological University
Current assignee: Shaanxi Yuecarbon New Materials Technology Co.,Ltd.
Priority date: 2019-04-28
Filing date: 2019-04-28
Publication date: 2020-11-27
Anticipated expiration: 2039-04-28
Also published as: CN110106470A

Abstract

The invention relates to a preparation method of a low-stress diamond-like carbon film. The object of the present invention is to reduce the optical transmittance and hardness of a DLC film while ensuring the optical transmittance and hardnessIts stress. The provided technical scheme is as follows: a method for improving the laser damage resistance of diamond-like carbon film is to form a closed-loop magnetic path on the surface of DLC and dielectric film and to make the magnetic flux of the closed loop have the maximum gradient. The device that provides includes the magnetic conduction frame, is provided with a pair of permanent magnet in the frame, first permanent magnet and second permanent magnet, and the distance of first permanent magnet and second permanent magnet is adjustable. By using the method of the invention, the damage threshold value of the DLC film can be from 0.57J/cm²Increased to 1.23J/cm². The dielectric film can reduce the laser damage area by about 50 percent.

Description

Preparation method of low-stress diamond-like carbon film

Technical Field

The invention belongs to the field of stress regulation and control of an anti-reflection protective film for an infrared optical transmission window, and particularly relates to a preparation method of a low-stress diamond-like carbon film.

Background

Missile and satellite guidance systems, infrared observation windows of various vehicles, aircrafts and vehicles, base materials (such as Ge, Si, ZnS, KBr and the like) of the missile and satellite guidance systems are generally soft in texture, easy to scratch, easy to absorb moisture and difficult to resist corrosion of a severe environment, and an antireflection protective film must be deposited on the surface of the base materials in order to reduce the optical energy loss of an infrared system and improve the signal-to-noise ratio of infrared signals. Once the film of the infrared window has cracks or falls off, the light energy loss and the image quality of the whole system are deteriorated, and even the catastrophic damage such as vacuum explosion of optical elements can be caused, so that the system is paralyzed. Therefore, as a film material for infrared windows, not only high abrasion resistance and salt mist and acid-base corrosion resistance are required, but also optical properties such as optical loss and infrared transmittance are required.

DLC (Diamond-like carbon) film is an amorphous carbon film because carbon atoms in diamond and graphite are sp atoms, respectively³C-C clusters and sp²The C-C cluster form is bonded, so that the DLC film has the property of being between diamond and graphite. DLC films are classified into amorphous carbons (a-C) according to the bonding mode of carbon atoms in the film and whether they contain H or not]Film, H-containing amorphous carbon (a-C: H)]Films and tetrahedral amorphous carbon (ta-C)]Three films are adopted. The DLC films of the a-C and a-C: H types show good infrared transmission performance in an atmospheric window of 1-2.5 mu m. As an anti-reflection protective film, the a-C and a-C H-type DLC film has been successively applied to systems such as a periscope infrared window, an army sight infrared window, an aircraft front-view infrared window, a remote sensing satellite receiving window and the like.

DLC films coated on the surface of infrared devices typically fail in service by substrate deformation, film delamination and film cracking. It is widely believed that the stress on the DLC film is too great and the film-based bonding is unstable. The stress of the DLC film with the thickness of 1.4 mu m or more prepared by Siegal and the like is about 10 GPa, and the stress imbalance causes the film layer to crack locally, the substrate to deform and the film to fall off under a load state; robertson et al have considered that when the compressive stress of the DLC film is larger than the adhesion between the DLC film and the substrate, film-base detachment occurs, but the stress control mechanism has not been clarified; ferrari et al found sp in the film³The bond content ranges from 20 percent to 85 percent, the stress value ranges from 2 GPa to 19 GPa, and sp is considered³The bond content is the main cause of stress influence, and the influence of ion bombardment energy reaching the substrate during deposition on the C-C bonding structure must be considered.

From the above studies, it can be seen that the stress of the DLC film is a main cause affecting the application stability thereof. Therefore, for the application stability of the DLC film, the problem of stress control thereof is to be solved first. The conventional method comprises the following steps: (1) and the DLC bonding process is controlled by process optimization to realize stress regulation and control. Molecule dynamic model based on first principleTo study sp in diamond-like thin film²-sp³The bonding process of the spatial structure stability of orbital hybridization is considered that the stress property of the film depends on the balance relation of attraction and repulsion inside atoms, and the stress is controllable. Loisel et al studied the preparation technique, technological parameters and the like of diamond-like carbon film sp²、sp³The bond structure and the microscopic properties. The method obtains the film stress less than 2.7GPa by changing parameters such as radio frequency power, direct current bias voltage, substrate temperature and the like, but has the problem that the hardness is reduced along with the film stress; (2) stress regulation and control are realized through doping, gradient films, transition layer structures and the like. Kulikovsky et al found that the atomic number fraction of silicon in silicon-doped a-C films can affect film hardness and stress. Williams et Al find that the doping of metallic Al which forms weak chemical bonds with carbon is beneficial to increasing the thermodynamic driving force for separating out graphitized carbon phase from the film and can also reduce the internal stress of the DLC film; paul et al, through the doping of nano microcrystalline gold particles, the film stress is reduced from 2.3 GPa to 0.48 GPa; the Kingling and the like realize that the DLC film has lower stress and can be reliably deposited on the surface of the aluminum alloy in a large area through a Ti/TiN/Si/(TiC/a-C: H) functionalized gradient multilayer structure; the diamond-like film with low stress and controllable structure is prepared by researching titanium-silicon co-doping; wanaiying, etc., uses a small amount of metal (Cr, Ti, W) incorporated into the DLC film, reducing the stress of the film. The method has certain influence on parameters such as hardness, elastic modulus and the like of the DLC film, and changes the internal structure of the film, such as the formation of nano crystals.

In summary, it is an urgent problem to reduce the stress of the DLC film while ensuring the optical transmittance and hardness thereof.

Disclosure of Invention

The invention aims to provide a preparation method of a low-stress diamond-like carbon film, which reduces the stress of the DLC film on the basis of ensuring the optical transmittance and the hardness of the DLC film.

In order to achieve the aim, the invention provides a method for regulating and controlling the stress of a low-stress diamond-like carbon film, which takes double-sided polished Si and Ge as substrates and alternately deposits and grows a-C/a-C: H multilayer gradient structure filmFilm to obtain films with different sp³And sp²A hybrid DLC film.

The method comprises the following steps:

step one, preparing a substrate material and a target material:

the substrate material is selected from double-sided polished Si or Ge with high infrared band transmittance. The target material in the sputtering cavity is high-density graphite with the content of 99.99 percent, and the size of the target material is 50 multiplied by 5 mm.

Step two, sputtering preparation:

starting a mechanical pump power supply corresponding to the vacuumizing interface, starting the low vacuum gauge, starting the gate valve when the reading of the low vacuum gauge is less than 15Pa, then starting the molecular pump power supply, starting the high vacuum gauge when the reading of the low vacuum gauge is less than 0.5Pa, starting the molecular pump power supply, and enabling the vacuum degree to reach 2.0 multiplied by 10^-8After Pa, the high vacuum gauge is closed, the cavity starts to be heated until the temperature of the cavity is stable, after about 10 minutes, the high vacuum gauge is opened again, the reading of the high vacuum gauge is the background vacuum value, and the background vacuum degree is 2.0 multiplied by 10^-7Pa。

Step three, sputtering to generate a DLC film:

and turning on the power supply of the sputtering power supply cabinet to fully preheat the device for 30 minutes. And (3) charging a working gas source (Ar gas) into the cavity while preheating the sputtering power supply, and opening the needle valve to distribute gas. After the radio frequency power supply is preheated, a sputtering button is started, the ion source is adjusted to be matched with a knob of an argon gas source until glow is generated, and the reflection value is adjusted. When the glow is stabilized, the power knob and the bias knob are adjusted. After pre-sputtering for 10 minutes, the shutter was opened, and the a-C and a-C: H DLC films were alternately sputter-grown. The glow was stable and no apparent color change was observed throughout the experiment. The shutter is closed, the incident power is lowered to 0, and then the power supply is sequentially turned off.

Compared with the prior art, the invention has the beneficial effects that:

1. based on a Physical Vapor Deposition (PVD) method only, Si and Ge which are polished on two sides are used as substrates, intermittent H ion layered implantation is assisted, C-H bonds in the DLC film are replaced by C-C bonds, ion energy and dosage are controlled, and a-C/a-C is alternately deposited and grownChanging the structure of the thin film to obtain films with different sp³And sp²A hybrid DLC film capable of realizing sp pair²/sp³Precise control of C-C (H) bonding properties, resulting in sp³High stress induced by hybridization of strong sigma bonds due to gaps or dislocation is relieved after H ions are replaced, stress regulation and control of the DLC film are realized, and application stability of the DLC film is improved.

2. The alpha-C grown by H ion replacing C atom in the method is a DLC film of H type, and still has good infrared transmittance; after the a-C/a-C-H multilayer gradient structure film is alternately deposited and grown, new impurities and absorption centers are not introduced, and the integral infrared transmittance of the DLC film is not reduced.

3. The DLC film with the a-C type is grown on the outermost layer, so that the high hardness characteristic of the film is reserved without reducing the hardness of the film.

Drawings

FIG. 1 is a schematic structural diagram of a thin film deposition apparatus provided in the present invention;

FIG. 2 is a schematic diagram of a graded structure of a H ion substitutional C atom grown DLC film according to the present invention;

fig. 3 is a graph of the optical constant measurement results provided by the present invention.

The reference numerals are explained below:

the method comprises the following steps of 1-target material, 2-rotating shaft, 3-ion source, 4-argon gas source, 5-vacuumizing interface, 6-heating substrate, 7-baffle, 8-working gas source, 9-magnetic control alternating magnetic pole and 10-magnet exciting coil. 11-a-C type DLC film, 12-a-C after replacing C atom by H ion, H type DLC film, 13-C-C cluster, 14-dislocation structure, 15-Si substrate, 16-impurity in DLC film, and 17-H ion replacing C atom.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention include, but are not limited to, the scope shown in the following examples.

In order to achieve the above object, the present invention provides a method for preparing a low stress diamond-like thin film by double-side polishingi and Ge are taken as substrates, intermittent H ion layered injection is assisted, C-H bonds in the DLC film are substituted for C-C bonds, ion energy and dosage are controlled, a-C/a-C: H multilayer gradient structure film is alternately deposited and grown, and films with different sp values are obtained³And sp²DLC film in hybrid state, realization of sp²/sp³Regulation of C-C (H) bonding properties to sp³High stress induced by hybridized strong sigma bonds due to gaps or dislocation is relieved after H ions are replaced; on the basis of the existing process parameters, DLC film samples with different physical properties are obtained by adjusting the process parameters.

A preparation method of a low-stress diamond-like carbon film comprises the following steps:

step one, preparing a substrate material and a target material:

Step two, sputtering preparation:

Step three, sputtering to generate a DLC film:

and turning on the power supply of the sputtering power supply cabinet to fully preheat the device for 30 minutes. And (3) charging a working gas source 8 (Ar gas) into the cavity while preheating the sputtering power supply, distributing gas, and opening the needle valve to an experimental set value of 40-80 sccm. After the radio frequency power supply is preheated, a sputtering button is started, and the knob of the ion source 3 and the argon source 4 are adjusted to be matched until glow is generated. When the glow is stabilized, the power knob 250 and 450W are adjusted, and the bias knob is adjusted to 90-130V. After sputtering for 10 minutes, the shutter 7 was opened, and formal sputtering was carried out for 60 minutes to grow an a-C type DLC film; opening an H ion source for auxiliary sputtering, wherein an a-C-H DLC film grows for 30 minutes; continuing sputtering for 60 minutes after the H ion source is closed, and opening the H ion source to assist sputtering for 30 minutes; the cycle lasts for 6 times according to the growth thickness requirement of the film; the glow was stable and no apparent color change was observed throughout the experiment. Closing the baffle 7, reducing the incident power to zero, closing the sputtering power supply on the power supply cabinet, reducing the bias voltage of the substrate 7 to room temperature, reducing the bias pressure valve to zero, closing the gas cylinder valve, closing the working gas source 8 connected between the gas cylinder and the cavity, opening the gate valve, discharging the working gas in the cavity, closing the molecular pump power supply, closing the mechanical pump power supply, closing the main power supply of the power supply cabinet, and closing the circulating water machine power supply.

Example (b): a preparation method of a low-stress diamond-like carbon film comprises the following specific steps:

step one, selecting a substrate material which is a double-sided polished (100) silicon wafer, and depositing a film under the same process conditions, wherein the total number of the silicon wafers is 9. Soaking the Si wafer in 5% FH solution for 5min before deposition, washing with clear water, ultrasonically cleaning the Si wafer with deionized water for 10min, ultrasonically cleaning the Si wafer in a mixed solution of acetone and absolute ethyl alcohol for 10min, and blow-drying with nitrogen for later use.

And (3) polishing and cleaning the surfaces of the target material 1, the baffle 7 and other parts by using sand paper, closing the baffle, placing 9 cleaned substrates on a heating substrate 6 in a magnetron sputtering cavity, and checking circulating water. The experiment adopted a high-density graphite target with a purity of 99.99%, the target size was 50 x 5mm, the target surface was cleaned with a brush before the target 1 was installed, and then the dust and impurities on the surface were removed with nitrogen.

Step two, starting a mechanical pump power supply corresponding to the vacuumizing interface 5, starting a low vacuum gauge, starting a gate valve when the indication number of the low vacuum gauge is less than 15Pa, then starting a molecular pump power supply, starting a high vacuum gauge when the indication number of the low vacuum gauge is less than 0.5Pa, starting the molecular pump power supply, and after about 10 hours, enabling the vacuum degree to reach 2.0 multiplied by 10^-8Pa. Turning off the high vacuum gauge and starting to align the chamberHeating until the temperature of the cavity is stable, opening the high vacuum gauge again after about 10 minutes, wherein the reading of the high vacuum gauge is the background vacuum value, and the background vacuum degree required by the experiment is 2.0 multiplied by 10^-7Pa, ready for sputtering.

And step three, turning on a power supply of the sputtering power supply cabinet to fully preheat the device for 30 minutes. And (3) charging a working gas source 8 (Ar gas) into the cavity while preheating the sputtering power supply, distributing gas, and opening the needle valve to an experimental set value of 40-80 sccm. After the radio frequency power supply is preheated, a sputtering button is started, and the knob of the ion source 3 and the argon source 4 are adjusted to be matched until glow is generated. When the glow is stabilized, the power knob 250 and 450W are adjusted, and the bias knob is adjusted to 90-130V. After sputtering for 10 minutes, the shutter 7 was opened, and formal sputtering was carried out for 60 minutes to grow an a-C type DLC film; opening an H ion source for auxiliary sputtering, wherein an a-C-H DLC film grows for 30 minutes; continuing sputtering for 60 minutes after the H ion source is closed, and opening the H ion source to assist sputtering for 30 minutes; the cycle lasts for 6 times according to the growth thickness requirement of the film; the glow was stable and no apparent color change was observed throughout the experiment. Closing the baffle 7, reducing the incident power to zero, closing the sputtering power supply on the power supply cabinet, reducing the bias voltage of the substrate 7 to room temperature, reducing the bias pressure valve to zero, closing the gas cylinder valve, closing the working gas source 8 connected between the gas cylinder and the cavity, opening the gate valve, discharging the working gas in the cavity, closing the molecular pump power supply, closing the mechanical pump power supply, closing the main power supply of the power supply cabinet, and closing the circulating water machine power supply.

The films of 9 samples were prepared by the above method, and the specific process parameters of each sample are shown in table 1.

Table 1: process parameter tables of the examples

As shown in fig. 1, the principle of the present invention is:

when the system is working, a certain current needs to be supplied to the exciting coil 10, and then the magnetic flux penetrating out of the target 1 of the unbalanced magnetic field generating deviceNot equal to the flux penetration, the sputtering system operates in a non-equilibrium mode. Microscopically, the motion of the plasma in the longitudinal excitation magnetic field 9 is a helical motion, but due to the small radius of rotation, macroscopically, it appears that the ions move along the magnetic field lines. The magnitude of the exciting current reflects to a certain extent the ion n bombarding the substrate_1/Atom n₀Ratio, n₁/ n₀Can be expressed as a scale of the degree of imbalance as n₁/ n₀ =0.71×J_SR, in the formula, J_SA current density of about 2mA/cm on the workpiece to be plated²R is the plating rate, about 0.1 nm/s. The ion/atom ratio of the substrate surface when depositing the DLC film was calculated from the above formula to be 14: 1.

The magnetron sputtering target 10 used in the experiment has a target surface size of 480mm × 80mm, and the target material is high-purity graphite. The horizontal magnetic induction intensity value generated by the permanent magnet of the target surface 1 is (40-60) mT in the sputtering runway area. The electromagnetic induction generated by the excitation coil is (8-12) mT, and although the value is only 10% -20% of that of the permanent magnet, the electromagnetic induction plays an important role in the film forming process. The maximum current of the excitation coil 8 can reach 180A. The sputtering working gas 6 is Ar and CH₄The gas mixture was controlled by a mass flow meter, and the distance of the work piece from the sputtering target was 150 mm.

In the experiment, when the vacuum degree of the bell jar reaches 5 multiplied by 10^-3And when Pa, cleaning the surface of the substrate by using argon ions with certain intensity, turning on a sputtering target power supply after cleaning is finished, and depositing and growing the DLC film on the substrate by using H ions and substitutional C atoms at room temperature.

The cause of the generation of stress was analyzed as shown in fig. 2, and the influence of stress on the microstructure of the DLC film was plotted based on the analysis results. During the film growth process, residual gas also remains as an impurity in the film to generate interstitial atoms, and sputtering of target particles during sputtering causes generation of defects such as dislocations, which affects the structure of the film. The accumulation of defects during film deposition creates stress that places the alignment between the molecules or atoms of the film in an unstable state. And H ion injection can reduce the internal defects of the film, so that partial atoms or molecules can restore a stable state, thereby reducing the stress of the DLC film.

As shown in FIG. 3, using this method and the above-mentioned process parameters, 9 samples of DLC film grown by alternating a-C/a-C: H sputtering were prepared on a Si substrate placed on a heating substrate 6 in a magnetron sputtering chamber, and were subjected to extinction coefficient measurement. Tests show that the extinction coefficients of the samples are very small, wherein the extinction coefficient of the No. 8 sample is the minimum, and the light absorption loss of the DLC film on the surface is small; the four samples are subjected to film stress test and theoretical transmittance calculation, the theoretical infrared transmittance of the samples is greater than 92%, and the maximum stress is 1.04GPa, and the results are shown in Table 2.

Table 2: theoretical infrared transmission and corresponding stress of thin film

Furthermore, the invention can effectively reduce the film stress on the premise of keeping the infrared transmittance of the DLC film.

Claims

1. A preparation method of a low-stress diamond-like carbon film is characterized by comprising the following steps:

using double-side polished Si and Ge as substrate materials, alternately depositing and growing a-C/a-C: H multilayer gradient structure film to obtain films with different sp³And sp²A hybrid DLC film;

the alternate deposition growth comprises the following specific steps:

starting a mechanical pump power supply corresponding to the vacuumizing interface, starting the low vacuum gauge, starting the gate valve when the reading of the low vacuum gauge is less than 15Pa, then starting the molecular pump power supply, starting the high vacuum gauge when the reading of the low vacuum gauge is less than 0.5Pa, starting the molecular pump power supply, and enabling the vacuum degree to reach 2.0 multiplied by 10^-8After Pa, the high vacuum gauge is closed, the cavity starts to be heated until the temperature of the cavity is stable, after 10 minutes, the high vacuum gauge is opened again, the reading of the high vacuum gauge is the background vacuum value, and the background vacuum degree is 2.0 multiplied by 10^-7Pa; turning on a power supply of the sputtering power supply cabinet to fully preheat the device for 30 minutes; preheating at sputtering power supplyMeanwhile, a working gas source is filled into the cavity, and the needle valve is opened to distribute gas; after the radio frequency power supply is preheated, starting a sputtering button, adjusting a knob of an ion source and an argon gas source to be matched until glow is generated, adjusting a reflection value, and adjusting a power knob and a bias knob after the glow is stable; after pre-sputtering for 10 minutes, opening a baffle plate, and starting to alternately sputter and grow the a-C and a-C: H DLC film; in the whole experiment process, the glow is continuously and stably, no obvious color change exists, the baffle plate is closed, the incident power is reduced to 0, and then the power supply is sequentially closed.

2. The method for preparing a low stress diamond-like carbon film according to claim 1, wherein:

the target used in the sputtering process is 99.99% of high-density graphite, and the size of the target is 50 x 5 mm.